在 web 项目中，可以通过配置过滤器解决跨域问题

1、创建过滤器类 AccessFilter 实现 servlet.Filter

package com.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

public class AccessFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain fc)
			throws IOException, ServletException {
                //解决跨域核心代码
		HttpServletResponse httpServletResponse = (HttpServletResponse) res;
		httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
		httpServletResponse.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
		httpServletResponse.setHeader("Access-Control-Max-Age", "3600");
		httpServletResponse.setHeader("Access-Control-Allow-Headers", "x-requested-with");
		fc.doFilter(req, res);

	}

	@Override
	public void destroy() {

	}

}

2、在web.xml 文件中配置刚刚创建的过滤器 AccessFilter

<filter>
    <filter-name>crossorigin</filter-name>
    <filter-class>com.filter.AccessFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>crossorigin</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>